<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>04_固定定位</title>
  <style>
    .fu{
      background-color: #ff0;
    }
    .fu>div{
      width: 100px;
      height: 100px;
    }
    .z1{background-color: #f00;}
    .z2{background-color: #0f0;/* 固定定位：会脱离文档流释放布局空间，移动参照物为html根元素 */
        position: fixed;
        left: 0;
        bottom: 0;}
    .z3{background-color: #00f;}
  </style>
</head>
<body>
<div class="fu">
  <div class="z1"></div>
  <div class="z2"></div>
  <div class="z3"></div>
</div>
</body>
</html>